Cell based integrated circuit and unit cell architecture therefor

ABSTRACT

In a unit cell, a first conductive type active region and a second conductive type active region are provided. Those two active regions extend in a first direction. Each of the active regions has first and second ends thereof. The first end of the second conductive type active region opposes the second end of the first conductive type active region. A poly-silicon pattern is provided to extend in the first direction across the first conductive type active region and second conductive type active region. A first contact region is arranged adjacent the first end of the first conductive type active region in the first direction. A second contact region is arranged adjacent the second end of the second conductive type active region in the first direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of application Ser. No. 09/525,330,filed Mar. 13, 2000, which is hereby incorporated by reference in itsentirety for all purposes.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to cell based integrated circuits and unitcell architecture for such circuits, which result in significantimprovement of the degree of integration.

BACKGROUND OF THE INVENTION

Cell based integrated circuit technology and cell architecture for suchcircuits have been developed as quick-turns integrated circuit (IC)design methodologies in which pre-designed circuit units or cells arewired together to rapidly implement a new IC functionality. Thepre-designed circuit elements are called macro cells which are made byinterconnecting unit cells.

A conventional unit cell includes a P-type active region (PMOStransistor) and an N-type active region (NMOS transistor), which arearranged in a first direction. A pair of poly-silicon regions is formedon each of the P-type and N-type active regions. Those poly-siliconregions are extending in parallel to each other in the first direction.The unit cell also includes first and second substrate contact regions,which are arranged in parallel to the P-type active region and N-typeactive region respectively.

When a circuit, such as a macrolibrary, is made, the poly-siliconregions on the P-type active region are connected to the poly-siliconregions on the N-type active region with conductive lines.

According to the conventional unit cell, power line (Vdd) and groundline (Vss) across the P-type active region and N-type active region;therefore the arrangement of conductive lines becomes complicated. Toprevent intersection between signal lines and power line/ground line,the signal lines should be formed on a different layer from the powerline and ground line. As a result, it becomes difficult to increase thedegree of integration of the IC.

Further, conductive lines connecting the poly-silicon lines on theP-type active region and N-type active regions may across the signallines, therefore the arrangement of conductive lines becomescomplicated. To prevent intersection between such conductive lines andthe signal lines, the signal lines should be formed on a differentlayer. As a result, it becomes difficult to increase the degree ofintegration of the IC.

OBJECTS OF THE INVENTION

Accordingly, an object of the present invention is to provide a methodfor designing a unit cell that contributes for increasing the degree ofintegration of the integrated circuit.

Another object of the present invention is to provide a unit cell thatcontributes for increasing the degree of integration of the integratedcircuit.

Further object of the present invention is to provide an integratedcircuit of which the degree of integration can be increased.

Additional objects, advantages and novel features of the presentinvention will be set forth in part in the description that follows, andin part will become apparent to those skilled in the art uponexamination of the following or may be learned by practice of theinvention. The objects and advantages of the invention may be realizedand attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, in a method fordesigning a unit cell, a first conductive type active region and asecond conductive type active region are provided. Those two activeregions are arranged to extend in a first direction. Each of the activeregions has first and second ends thereof. The first end of the secondconductive type active regions is opposing to the second end of thefirst conductive type active region. In the method, a poly-siliconpattern is provided to extend in the first direction across the firstconductive type active region and second conductive type active region.A first contact region is arranged adjacent the first end of the firstconductive type active region in the first direction. A second contactregion is arranged adjacent the second end of the second conductive typeactive region in the first direction.

Preferably, the first conductive type active region is formed to have aprojecting region at the first end, which extends in the first directiontoward the first contact region; and the second conductive type activeregion is formed to have a projecting region at the second end, whichextends in the first direction toward the second contact region.

The poly-silicon pattern may extend in the first direction continuouslywithout any break therein.

According to a second aspect of the present invention, a unit cell thatis designed by a method according to the above described first aspect ofthe present invention.

According to a third aspect of the present invention, an integratedcircuit that is made by a unit cell according to the above describedsecond aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a conventional unit cell architecture.

FIG. 2 is a plan view showing an inverter that is made with theconventional unit cell, shown in FIG. 1.

FIG. 3 is a plan view showing a unit cell architecture according to afirst preferred embodiment of the present invention.

FIG. 4 is a plan view showing a unit cell architecture according to asecond preferred embodiment of the present invention.

FIG. 5 is a plan view showing a unit cell architecture according to athird preferred embodiment of the present invention.

FIG. 6 is a plan view showing a unit cell architecture according to afourth preferred embodiment of the present invention.

FIG. 7 is a plan view showing a two-input NAND gate that is made withthe unit cell, shown in FIG. 3.

FIG. 8 is a plan view showing a multiplexor that is made with the unitcell, shown in FIG. 3.

DETAILED DISCLOSURE OF THE INVENTION

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration specific preferredembodiments in which the inventions may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that otherembodiments may be utilized and that logical, mechanical and electricalchanges may be made without departing from the spirit and scope of thepresent inventions. The following detailed description is, therefore,not to be taken in a limiting sense, and scope of the present inventionsis defined only by the appended claims.

For better understanding of the present invention, a conventionaltechnology is first described. FIG. 1 shows a conventional unit cellarchitecture. The unit cell includes an N-type well contact region 10(N+ contact region) for Vdd (distributed power); a substrate contactregions 12 (P+ contact region) for Vss (ground); a P+ active region 18;an N+ active region 20; and poly-silicon patterns 22 a, 22 b, 22 c and22 d. The P+ active region 18 is formed on an N-type well region 26.

The P+ active region 18 and N+ active region 20 are arranged to extendin a first direction, between the top and bottom in the drawing. TheN-type well contact region 10 is arranged in parallel to the P+ activeregion 18. The substrate contact region 12 is arranged in parallel tothe N+ active region 20. Each of the poly-silicon patterns 22 a-22 dextends in the first direction, between the top and bottom of thearchitecture.

The N-type well contact region 10 is connected to a power supply (Vdd)line 14, which extends in a second direction orthogonal to the firstdirection. In the same manner, the substrate contact region 12 isconnected to a ground (Vss) line 16, which extends in the seconddirection.

FIG. 2 shows an inverter that is made with the conventional unit cell,shown in FIG. 1. In the inverter, the P+ active region 18 and N+ activeregion 20 are connected to each other by a conductive line 32. Thepoly-silicon patterns 22 a and 22 c are connected to each other by aconductive line 30. One portion of the P+ active region 18 is connectedto the substrate contact region 10 by the power supply line 14. Oneportion of the N-type active region 20 is connected to the substratecontact region 12 by the ground line 16.

According to the conventional unit cell, the power line 14 and groundline 16 are arranged to across the P+ active region 18 and N+ activeregion 20 in the orthogonal direction; therefore the arrangement ofconductive lines becomes complicated. To prevent intersection betweensignal lines and power/ground lines, the signal lines should be formedon a different layer from the power line and ground line. As a result,it becomes difficult to increase the degree of integration of the IC.

Further, conductive lines connecting the poly-silicon patterns mayacross the signal lines, therefore the arrangement of conductive linesbecomes complicated. To prevent intersection between such conductivelines and the signal lines, the signal lines should be formed on adifferent layer. As a result, it becomes difficult to increase thedegree of integration of the IC.

FIG. 3 shows a unit cell architecture 100 according to a first preferredembodiment of the present invention. The unit cell 100 includes anN-type well contact region 110 (N+ contact region) for Vdd (distributedpower); a substrate contact regions 112 (P+ contact region) for Vss(ground); a P+ active region 118; an N+ active region 120; andpoly-silicon patterns 122 a and 122 b, including gate electrode portionand terminal.

The P+ active region 118 and N-type well contact region 110 are formedon an N-type well region 126.

Metal layers 111 and 113 are formed over the substrate contact region(N+ contact region) 110 and substrate contact region (P+ contact region)112, respectively. The substrate contact region 110 is provided withcontacts 110 a, which make electrical contact to the metal layer 111. Inthe same manner, the substrate contact region 112 is provided withcontacts 112 a, which make electrical contact to the metal layer 113.

The P+ active region 118 and N+ active region 120 are arranged to extendin a first direction, between the top and bottom of the architecture.The poly-silicon patterns 122 a and 122 b are arranged to extend in thefirst direction as well to across the P+ active region 118 and N+ activeregion 120. In other words, those two poly-silicon patterns 122 a and122 b extends continuously without any breaks between the P+ activeregion 118 and N+ active region 120.

The P+ active region 118 is formed to have first and second endsthereof, in which the first end is opposing to the N-type well contactregion 110. The P+ active region 118 is shaped to have a projectingregion 118 a at the first end thereof. In other words, the projectingregion 118 a extends toward the substrate contact region 110.

The N+ active region 120 is formed to have first and second endsthereof, which respectively oppose to the second end of the P+ activeregion 118 and the substrate contact region 112. The N+ active region120 is shaped to have a projecting region 120 a at the second endthereof. The projecting region 120 a extends toward the substratecontact region 112.

The N+ contact region 110 is arranged adjacent to the first end of theP+ active region 118 in the first direction. In the same manner, thesubstrate contact region 112 is arranged adjacent to the second end ofthe N+ active region 118 in the first direction.

In fabrication, the N type well region 126 is first formed, and then theP+ ions are introduced into the substrate to form the P+ active regions118 and the P+ contact regions 112. Then, N+ ions are introduced intothe substrate to form the N+ active region 120 and the N+ contact region110. The poly-silicon gate pattern including terminals 122 a and 122 bare formed, and then the metal layers 111 and 113 are formed over the N+contact region 110 and P+ contact region 112, respectively. The metallayers 110 and 118 are electrically connected to the N+ contact region110 and P+ contact region 112 via the contacts (or using through holes)110 a and 112 a, respectively. The metal layers 111 and 113 are to beconnected to another metal layer (second metal layer) using throughholes.

According to the unit cell 100, the contact regions 110 and 112 arearranged at the top and bottom ends of the architecture 100, so thatpower line and ground line are arranged to extend in the seconddirection without crossing the active regions 118 and 120. Therefore, itis not always required to form signal lines on a different layer toprevent intersection between those signal lines and the power/groundlines. Further, the poly-silicon patterns 122 a and 122 b extend throughthe P+ active region 118 and N+ active region 120, so that no conductiveline is necessary to connect the poly-silicon terminals to each other.Such architecture allows the integrated circuit to increase the degreeof integration.

FIG. 4 shows a unit cell architecture according to a second preferredembodiment of the present invention. The unit cell 200 includes anN-type well contact region 210 (N+ contact region) for Vdd (distributedpower); a substrate contact regions 212 (P+ contact region) for Vss(ground); a P+ active region 218; an N+ active region 220; andpoly-silicon patterns 222 a and 222 b.

The P+ active region 218 and N+ contact region 210 are formed on anN-type well region 226.

Metal layers 211 and 213 are formed over the contact regions 210 and212, respectively. The N+ contact region 210 is provided with contacts210 a for making electrical contact to the metal layer 211. In the samemanner, the P+ contact region 212 is provided with contacts 212 a formaking electrical contact to the metal layer 213.

The P+ active region 218 and N+ active region 220 are arranged to extendin a first direction, between the top and bottom of the architecture.The poly-silicon patterns 222 a and 222 b are arranged to extend in thefirst direction as well to across the P+ active region 218 and N+ activeregion 220. In other words, those two poly-silicon patterns 222 a and222 b extends continuously without any breaks between the P+ activeregion 218 and N+ active region 220. The poly-silicon layer (pattern)222 a is connected at the top and bottom ends to the contact regions 210and 212, respectively. In the same manner, the poly-silicon layer(pattern) 222 b is connected at the top and bottom ends to the substratecontact regions 210 and 212, respectively.

The P+ active region 218 is formed to have first and second endsthereof, in which the first end is opposing to the N+ contact region210. The N+ active region 220 is formed to have first and second endsthereof, which respectively oppose to the second end of the P+ activeregion 218 and the P+ contact region 212.

The N+ contact region 210 is arranged adjacent to the first end of theP+ active region 218 in the first direction. In the same manner, the P+contact region 212 is arranged adjacent to the second end of the N+active region 218 in the first direction.

In fabrication, the N type well region 226 is first formed, and then theP+ ions are introduced into the substrate to form the P+ active regions218 and the P+ contact regions 212. Then, N+ ions are introduced intothe substrate to form the N+ active region 220 and the N+ contact region210. The poly-silicon gate pattern including terminals 222 a and 222 bare formed, and then the metal layers 211 and 213 are formed over the N+contact region 210 and P+ contact region 212, respectively. The metallayers 210 and 213 are electrically connected to the N+ contact region210 and P+ contact region 212 via the contacts (or using through holes)210 a and 212 a, respectively. The metal layers 211 and 213 are to beconnected to another metal layer (second metal layer) using throughholes.

According to the unit cell 200, the contact regions 210 and 212 arearranged at the top and bottom ends of the architecture 200, so thatpower line and ground line are arranged to extend in the seconddirection without crossing the active regions 218 and 220. Therefore, itis not always required to form signal lines on a different layer toprevent intersection between those signal lines and the power/groundlines. Further, the poly-silicon patterns 222 a and 222 b extend throughthe P+ active region 218 and N+ active region 220, so that no conductiveline is necessary to connect the poly-silicon patterns to each other.Such architecture allows the integrated circuit to increase the degreeof integration.

FIG. 5 shows a unit cell architecture according to a third preferredembodiment of the present invention. The unit cell 300 includes a N-typewell contact region 310 (N+ contact region) for Vdd (distributed power);a substrate contact regions 312 (P+ contact region) for Vss (ground); aP+ active region 318; an N+ active region 320; and poly-silicon patterns322 a and 322 b. The P+ active region 318 is one grid longer than the P+active region 218 of the second preferred embodiment, shown in FIG. 4.

The P+ active region 318 and N+ contact region 310 are formed on anN-type well region 326.

The P+ active region 318 and N+ active region 320 are arranged to extendin a first direction, top and bottom in the drawing of FIG. 5. Thepoly-silicon patterns 322 a and 322 b are arranged to extend in thefirst direction as well to across the P+ active region 318 and N+ activeregion 320. In other words, those two poly-silicon patterns 322 a and322 b extends continuously without any breaks between the P+ activeregion 318 and N+ active region 320. The poly-silicon layer (pattern)322 a is connected at the top and bottom ends to the substrate contactregions 310 and 312, respectively. In the same manner, the poly-siliconlayer (pattern) 322 b is connected at the top and bottom ends to thecontact regions 310 and 312, respectively.

The P+ active region 318 is formed to have first and second endsthereof, in which the first end is opposing to the N+ contact region310. The N+ active region 320 is formed to have first and second endsthereof, which respectively oppose to the second end of the P+ activeregion 318 and the P+ contact region 312.

Metal layers 311 and 313 are formed over the contact regions 310 and312, respectively. The N+ contact region 310 is provided with contacts310 a for making electrical contact to the metal layer 311. In the samemanner, the P+ contact region 312 is provided with contacts 312 a formaking electrical contact to the metal layer 313.

The N+ contact region 310 is arranged adjacent to the first end of theP+ active region 318 in the first direction. In the same manner, the P+contact region 312 is arranged adjacent to the second end of the N+active region 318 in the first direction.

In fabrication, the N type well region 326 is first formed, and then theP+ ions are introduced into the substrate to form the P+ active regions318 and the P+ contact regions 312. Then, N+ ions are introduced intothe substrate to form the N+ active region 320 and the N+ contact region310. The poly-silicon gate pattern including terminals 322 a and 322 bare formed, and then the metal layers 311 and 313 are formed over the N+contact region 310 and P+ contact region 312, respectively. The metallayers 311 and 313 are electrically connected to the N+ contact region310 and P+ contact region 312 via the contacts (or using through holes)310 a and 312 a, respectively. The metal layers 311 and 313 are to beconnected to another metal layer (second metal layer) using throughholes.

According to the unit cell 300, the contact regions 310 and 312 arearranged at the top and bottom ends of the architecture 300, so thatpower line and ground line are arranged to extend in the seconddirection without crossing the active regions 318 and 320. Therefore, itis not always required to form signal lines on a different layer toprevent intersection between those signal lines and the power/groundlines. Further, the poly-silicon patterns 322 a and 322 b extend throughthe P+ active region 318 and N+ active region 320, so that no conductiveline is necessary to connect the poly-silicon patterns to each other.Such architecture allows the integrated circuit to increase the degreeof integration. Finally, since the P+ active regions 318 has longdimension, PMOS transistors formed in P+ active region 318 have improvedconductance.

FIG. 6 shows a unit cell architecture 400 according to a fourthpreferred embodiment of the present invention. The unit cell 400includes an N-type well contact region 410 (N+ contact region) for Vdd(distributed power); a substrate contact regions 412 (P+ contact region)for Vss (ground); a P+ active region 418; an N+ active region 420; andpoly-silicon patterns 422 a, 422 b and 422 c.

The P+ active region 418 and N+ contact region 410 are formed on anN-type well region 426.

The P+ active region 418 and N+ active region 420 are arranged to extendin a first direction, top and bottom in the drawing of FIG. 6. Thepoly-silicon patterns 422 a, 422 b and 422 c are arranged to extend inthe first direction. The poly-silicon pattern 422 a is extending acrossboth the P+ active region 418 and N+ active region 420. The poly-siliconpattern 422 b is extending across only the P+ active region 418, whilethe poly-silicon pattern 422 c is extending across only the N+ activeregion 420.

The P+ active region 418 is formed to have first and second endsthereof, in which the first end is opposing to the N+ contact region410. The P+ active region 418 is shaped to have a projecting region 418a at the first end thereof. In other words, the projecting region 418 aextends toward the N+ contact region 410.

The N+ active region 420 is formed to have first and second endsthereof, which respectively oppose to the second end of the P+ activeregion 418 and the P+ contact region 412. The N+ active region 420 isshaped to have a projecting region 420 a at the second end thereof. Theprojecting region 420 a extends toward the P+ contact region 412.

Metal layers 411 and 413 are formed over the N+ contact region 410 andP+ contact region 412, respectively. The N+ contact region 410 isprovided with contacts 410 a, which make electrical contact to the metallayer 411. In the same manner, the P+ contact region 412 is providedwith contacts 412 a, which make electrical contact to the metal layer413.

The N+ contact region 410 is arranged adjacent to the first end of theP+ active region 418 in the first direction. In the same manner, the P+contact region 412 is arranged adjacent to the second end of the N+active region 418 in the first direction.

In fabrication, the N type well region 426 is first formed, and then theP+ ions are introduced into the substrate to form the P+ active regions418 and the P+ contact regions 412. Then, N+ ions are introduced intothe substrate to form the N+ active region 420 and the N+ contact region410. The poly-silicon gate pattern including terminals 422 a, 422 b and422 c are formed, and then the metal layers 411 and 413 are formed overthe N+ contact region 410 and P+ contact region 412, respectively. Themetal layers 411 and 413 are electrically connected to the N+ contactregion 410 and P+ contact region 412 via the contacts (or using throughholes) 410 a and 412 a, respectively. The metal layers 411 and 413 areto be connected to another metal layer (second metal layer) usingthrough holes.

According to the unit cell 400, the substrate contact regions 410 and412 are arranged at the top and bottom ends of the architecture 400, sothat power line and ground line are arranged to extend in the seconddirection without crossing the active regions 418 and 420. Therefore, itis not always required to form signal lines on a different layer toprevent intersection between those signal lines and the power/groundlines. Further, the poly-silicon patterns 422 b and 422 c are formed tobe separated from each other, so that an integrated circuit can bedesigned flexibly as compared to the first preferred embodiment, shownin FIG. 3.

FIG. 7 shows a two-input NAND gate 500 that is made with the unit cell100, shown in FIG. 3. In the circuit 500, the N+ contact region 110 isconnected to outer portions of the P+ active region 118 by conductivelines 502 and 504. One of the outer portions of the P+ active region 118is connected to the poly-silicon pattern 122 a by a conductive line 506.An inner portion of the P+ active region 118 is also connected to one ofthe outer portions of the N+ active region 120 by a conductive line 510.The poly-silicon pattern 122 b is connected to the other outer portionof the N+ active region 120 by a conductive line 508. The other outerportion of the N+ active region 120 is also connected to the P+ contactregion 112 by a conductive line 512.

FIG. 8 shows a multiplexer that is made with the unit cells 100, shownin FIG. 3. In FIG. 8, a reference numeral 602 indicates a N type wellregion.

According to the present invention, substrate contact regions arearranged at the top and bottom ends of unit cell architecture, theintegrated circuit is improved in degree of integration. Further, whenpoly-silicon patterns are arranged to extend through P+ active regionand N+ active region, no conductive line is necessary to connect thepoly-silicon patterns to each other. That also allows the integratedcircuit to increase the degree of integration.

1. A method of designing an integrated circuit, comprising: providing aunit cell on a substrate, the unit cell including a first active region,which extends in a first direction to have first and second endsthereof, a second active region, which extends in the first direction tohave first and second ends thereof, the first end of the second activeregion opposing the second end of the first active region, a pair ofconductive patterns, each of which extends in the first direction acrossthe first active region and the second active region, wherein the firstactive region is divided into three first regions by the pair ofconductive patterns and the second active region is divided into threesecond regions by the pair of conductive patterns, a first contactregion formed in a well region and arranged directly adjacent to firstends of each of the three first regions in the first direction, and asecond contact region formed in the substrate and arranged directlyadjacent to second ends of each of the three second regions in the firstdirection; and providing conductive lines to selectively connect thefirst and second regions to each other.
 2. A method according to claim1, wherein the first active region is formed to have a first projectingregion at the first end thereof, which extends in the first directiontoward the first contact region, and the second active region is formedto have a second projecting region at the second end thereof, whichextends in the first direction toward the second contact region.
 3. Amethod according to claim 1, wherein the pair of conductive patternsextend in the first direction continuously with no break therein.
 4. Amethod according to claim 1, wherein the pair of conductive patterns areformed to be in contact with the first and second contact regions.
 5. Amethod according to claim 1, wherein a plurality of conductive patternsgreater than two are provided, and each is formed to be in contact withthe first and second contact regions.
 6. A method according to claim 1,wherein the plurality of conductive patterns comprise two line regionsdivided between the first active region and the second active region. 7.A method according to claim 1, further comprising providing a powersupply voltage to the first contact region.
 8. A method according toclaim 1, further comprising providing a ground to the second contactregion.
 9. A method of designing a unit cell on a substrate, which isused for making an integrated circuit, comprising: providing a firstconductive type active region, which extends in a first direction tohave first and second ends thereof; providing a second conductive typeactive region, which extends in the first direction to have first andsecond ends thereof, the first end of the second conductive type activeregion opposing the second end of the first conductive type activeregion; providing a pair of poly-silicon patterns each extendingcontinuously in parallel to each other in the first direction across thefirst conductive type active region and the second conductive typeactive region, wherein the first conductive type active region isdivided into three first regions by the pair of poly-silicon patternsand the second conductive type active region is divided into threesecond regions by the pair of poly-silicon patterns; providing a firstcontact region that is formed in a well region and arranged directlyadjacent to first ends of each of the three first regions in the firstdirection; and providing a second contact region that is formed in thesubstrate and arranged directly adjacent to second ends of each of thethree second regions in the first direction, wherein the firstconductive type active region is formed to have a first projectingregion at the first end thereof which extends in the first directiontoward the first contact region, the second conductive type activeregion is formed to have a second projecting region at the second endthereof which extends in the first direction toward the second contactregion, and the poly-silicon patterns are formed to be in contact withnone of the first and second contact regions.
 10. A method of making anintegrated circuit comprising: designing a unit cell; andinterconnecting portions of the unit cell to form the integratedcircuit, said designing a unit cell comprising providing a first activeregion in a substrate, the first active region extending lengthwise in afirst direction to have first and second ends, providing a second activeregion in the substrate, the second active region extending lengthwisein the first direction to have first and second ends, the first end ofthe second active region being directly adjacent the second end of thefirst active region, providing a pair of poly-silicon patterns eachextending continuously in parallel to each other lengthwise in the firstdirection across the first active region and the second active region,providing a first contact region having a plurality of first contacts,the first contact region being directly adjacent along an entire widthof the first end of the first active region, and providing a secondcontact region having a plurality of second contacts, the second contactregion being directly adjacent along an entirety of the second end ofthe second active region.
 11. A method according to claim 10, whereinsaid designing a unit cell further comprises: providing the first activeregion as having a first projecting region at the first end thereofwhich extends in the first direction toward the first contact region;and providing the second active region as having a second projectingregion at the second end thereof which extends in the first directiontoward the second contact region.
 12. A method according to claim 11,wherein said designing a unit cell further comprises providing thepoly-silicon patterns so as not to be in contact with the first andsecond contact regions.
 13. A method according to claim 10, wherein saiddesigning a unit cell further comprises: providing a power supply to thefirst contact region; and providing a ground to the second contactregion.